Lorenzo-Torres A, et al. J Vet Sci. 2022 Oct;23:e87. https://doi.org/10.4142/jvs.22168

For many years it has been sought to increase the reproductive efficiency of livestock using biotechnologies such as embryo bisection. However, despite its potential in livestock, its level of adoption is limited. The present work reviews the importance of demi-embryo reconstitution, after bisection, and the main factors that limit its success in livestock. It is possible to increase its level of adoption if it is possible to increase the efficiency currently obtained with this technique, this can be achieved by making a more precise selection of the embryos subjected to bisection. Embryo quality is one of the most important factors related to the potential to reconstitute into viable demi-embryos after bisection, which can be used with greater reliability in embryo transfer programs.

The corpus luteum (CL) is a transient gland that can directly influence follicular dynamics and oocyte quality. The objective of this study was to evaluate the influence of the absence or presence of a small (≤3 mm), medium (4–8 mm), or large (>8 mm) CL in slaughterhouse ovaries on in vitro embryo production. Cumulus–oocyte complexes (COCs) were collected from each group of ovaries and matured in TCM-199 medium, plus hormones and fetal bovine serum. Fertilization was performed with fresh semen from a Katahdin ram of known fertility. Embryo development was carried out in commercial sequential media for 72 and 96 h, until the blastocyst stage. The number of follicles (2–6 mm in diameter) and COCs were influenced by the presence of CL, which was higher (p < 0.05) in the Large CL group (5.51 ± 0.33 and 3.62 ± 0.27) compared to the Without CL group (4.54 ± 0.19 and 2.62 ± 0.14, respectively), with no difference between the CL sizes. Likewise, the diameter and area of the COCs were higher in the Small CL group of ovaries compared to the Without CL group. In the Large CL group of ovaries, 9% more morulae (p < 0.05) were obtained compared to the Without CL group; in the Medium CL group, 13% more blastocysts were obtained compared to the Without CL group. However, in the hatching capacity and diameter of blastocysts, no statistical difference was evident (p > 0.05). In conclusion, the presence and size of the CL in the ovaries of slaughtered sheep influence the productive efficiency of embryos in vitro under the conditions in which the present study was carried out.